Recently, as ubiquitous society appears, the signal transmission rate of information processing apparatuses and communication apparatuses has been improved, and the size thereof has been reduced. In servers, work stations, PCs, mobile phones, game consoles and the like, MPUs (micro processing units) have become faster, are more multifunctional and are more complexed, and storage devices, such as memory, have become faster.
However, electromagnetic wave noise radiated from these apparatuses or conductive noise passing through a conductor in the apparatuses cause malfunction of the apparatuses or another apparatuses. As one countermeasure against this problem, an electromagnetic wave shield function has been applied to a flexible printed wiring board.
As flexible printed wiring boards having the electromagnetic wave shield function, for example, the following flexible printed wiring boards have been proposed.
(1) A flexible printed wiring board, in which an undercoat layer, a shield layer to which conductive paste including metal powder is applied, and an overcoat layer are provided in this order on a copper foil wiring circuit on a surface of a heat resistant plastic film, and a ground pattern of the copper foil wiring circuit and the shield layer are electrically connected to each other at a predetermined distance through the undercoat layer (Patent Document 1).
(2) A flexible printed wiring board, in which an electromagnetic wave shield film provided with a metal thin film layer and a conductive adhesive layer including a metal filler in this order on one surface of a coverlay film is provided on a substrate film provided with an insulating layer for insulating a printed circuit other than a part of a ground circuit in the printed wiring board so that the conductive adhesive layer is adhered to the insulating layer and a part of the ground circuit (Patent Document 2).
However, the above-described flexible printed wiring boards (1), (2) have the electromagnetic wave shield function, but cannot suppress conductive noise passing through the conductive layers of the flexible printed wiring boards.
Patent Document 1: Japanese Patent Application Laid-Open No. Hei 2-33999.
Patent Document 2: Japanese Patent Application Laid-Open No 2000-269632.